The present invention relates to a magnetoresistive transducer, and more particularly to a magnetoresistive read head utilizing a giant magnetoresistance effect for sensing signal magnetic fields to read out magnetic information stored in a magnetic recording medium
The magnetoresistive head utilizing the magnetoresistive effect has a high sensitivity to signal magnetic fields, for which reason the magnetoresistive head is used for a high density magnetic recording. In the prior arts, it had been known that the magnetoresistive head has a magnetic layer which exhibits an anisotropic magnetoresistive effect. Such anisotropic magnetoresistive head has an electrical resistance which varies in proportion to a square of cosine of an angle defined between a direction of a current to be supplied to a magnetoresistive material and a direction of magnetization of the magnetoresistive material.
The magnetic recording device allows the magnetoresistive material to vary in magnetization direction in accordance with signal magnetic fields from a magnetic recording medium. This variation in magnetization direction of the magnetoresistive material causes a variation in resistance of the magnetoresistive material and also causes variations in current and voltage, for which reason the magnetic recording device can read out magnetic data or information from the magnetic recording medium.
Recently, in place of the above a giant magnetoresistance effect was discovered in a multi-layered structure wherein a non-magnetic layer is sandwiched between ferromagnetic metal layers. This giant magnetoresistance effect is caused in a multi-layer structure of Fe/Cr or Co/Cu showing an anti-ferromagnetic coupling. This giant magnetoresistance effect is also caused in another multi-layer structure of a free ferromagnetic layer/non-magnetic layer/pinned ferromagnetic layer. In the giant magnetoresistance effect, an electrical resistance varies in proportional to a cosine of an angle defined between magnetization directions of two ferromagnetic layers separated by a non-magnetic layer, but independently from a current direction.
In Japanese laid-open patent publication No. 4-358310, it is disclosed that the magnetic head utilizes a giant magnetoresistance effect. FIG. 1 is a schematic view illustrative of a conventional magnetoresistive sensor utilizing the giant magnetoresistance effect for sensing signal magnetic fields. The conventional magnetoresistive sensor comprises first and second ferromagnetic layers 101 and 103 separated by a non-magnetic metal layer 102 and an anti-ferromagnetic layer 104 adjacent to the second ferromagnetic layer 103 for pinning magnetization of the second ferromagnetic layer 103 by exchange-coupling. The first ferromagnetic layer 101 has a magnetization direction which is perpendicular to the pinned magnetization direction of the second ferromagnetic layer 103. Namely, the first ferromagnetic layer 101 serves as a ferromagnetic free layer. The second ferromagnetic layer 103 serves as a ferromagnetic pinned layer.
The largest linear response and the widest dynamic range can be obtained when the second ferromagnetic layer 103 has a pinned magnetization direction which is parallel to a direction of signal magnetic fields whilst the first ferromagnetic layer 101 has a magnetiztion direction which is perpendicular to the direction of the signal magnetic fields. Only the magnetization direction of the first ferromagnetic layer 101 is free to rotate so that an angle defined between the magnetization directions of the first and second ferromagnetic layers 101 and 103 varies. This variation in angle defined between the magnetization directions of the first and second ferromagnetic layers 101 and 103 causes a variation in electrical resistance, for which reason the variation in electrical resistance is detectable.
The above magnetic head or magnetic transducer utilizing the giant magnetoresistance effect has the following problems. It is required that the magnetization direction of the second ferromagnetic layer 103 is pinned in a direction parallel to the direction of the signal magnetic fields. The anti-ferromagnetic layer 104 is used for pinning the magnetization direction of the second ferromagnetic layer 103. Those layers are required to be heated up to a temperature near a Neel temperature for magnetic polarization in a direction parallel to the direction of the signal magnetic fields Ps. Those temperature rising and subsequent magnetic polarization processes might provide influences to the magnetic properties of the other parts of the magnetic head or transducer.
FIG. 2 is a fragmentary cross sectional elevation view illustrative of a magnetic head comprising an inductive portion for recording informations into a magnetic recording medium 100 (FIG. 1) and a giant magnetoresistance effect sensor portion for reading out the informations from the magnetic recording medium 100. The magnetic head normally has not only the magnetoresistive sensing portion but also the following elements. Bottom and top shielding layers 111 and 112 are provided for improvement in recording density in bit direction. Bottom and top pole layers 113 and 114 are provided for recording signals into the magnetic medium 100. A second anti-ferromagnetic layer 108 is further provided for generating a longitudinal bias magnetic field. As well illustrated in FIG. 2, the top shielding layer 112 and the bottom pole layer 113 are a common single layer.
In the high frequency range, in order to record and reproduce the magnetic signal into the magnetic medium, it is required that easy-axis of the top and bottom shielding layers 112 and 111 as well as the top and bottom pole layers 114 and 113 is perpendicular to the direction of the signal magnetic fields. Those magnetic layers are controlled in magnetic anisotropy so as to have a magnetization easy axis in a desired direction by growth of the magnetic layers in a magnetic field. However, the temperature rising and subsequent magnetic polarization processes for the anti-ferromagnetic layer 104 may disturb the magnetization easy-axis.
Namely, if the temperature rising and subsequent magnetic polarization processes for the anti-ferromagnetic layer 104 are made immediately after the anti-ferromagnetic layer 104 was formed, then the magnetization easy-axis of the bottom shielding layer 111 is disturbed. Even if the temperature rising and subsequent magnetic polarization processes for the anti-ferromagnetic layer 104 are made immediately after all of the layers were formed, then the magnetization easy-axis of the top and bottom shielding layers 112 and 111 as well as the top and bottom pole layers 114 and 113 is disturbed. As a result, over-write characteristic is deteriorated and a half width of the reproduced waveform is widened.
By contrast, the magnetization easy axis of the top and bottom shielding layers 112 and 111 as well as the top and bottom pole layers 114 and 113 can return to the direction perpendicular to the signal magnetic fields by applying a magnetic field in a direction perpendicular to the direction of the signal magnetic field and further optionally increasing a temperature of the layer, However, those processes for applying the magnetic field in the direction vertical to the signal magnetic fields and any subsequent temperature rising might weaken the pinning of the magnetization direction of the second ferromagnetic layer 103.
Even as described above the second anti-ferromagnetic layer 108 is provided for domain stabilization of the first ferromagnetic layer 101. The magnetic anisotropy of the second anti-ferromagnetic layer 108 is also oriented in a direction perpendicular to the signal magnetic fields "Ps", for which reason the temperature rising and magnetic polarization for pinning the second ferromagnetic layer 103 might disturb the magnetization easy axis.
In the above circumstances, it had been required to develop a novel magnetoresistive head utilizing a giant magnetoresistance effect and having a large linear responsibility without strong pinning of the magnetization in parallel to the signal magnetic fields.